166 Leyton and Sherrington 



(36) is elicitable from this region much less easily and regularly than are 

 the ordinary motor responses evocable from the precentralis motor field. 

 Moreover, the points which here yield it seem, as tested by the electrode, 

 to lie in a scattered manner, not constituting a continuo>tis field of excit- 

 able points. Examination of the region shows that reacting points are 

 most numerous along the area bordering the posterior part of calcarine 

 fissure, and therefore on the mesial face of the hemisphere, but both in 

 chimpanzee and gorilla the response was obtained also from a few points 

 of the lateral face of the hemisphere at its occipital pole ; the experiments 

 giving this were on quite young animals, except in the case of one adole- 

 scent chimpanzee. 



The other region whence eye-opening is elicitable, the frontal, is a large 

 one. It embraces a considerable part of the 2nd and 3rd frontal con- 

 volutions, and seems separated from the " precentralis motor region " by 

 an intervening strip of "silent" cortex, although this strip is sometimes 

 encroached on almost to extinction. Elicitation of eye-opening from this 

 region, like its elicitation from the occipital field, though apparently in a 

 less degree, is irregular, and requires stronger faradic currents than are 

 required for exciting motor responses from precentralis region. The move- 

 ment when evoked has commonly a more deliberate execution, and the 

 points which yield it are in any one experiment scattered in discrete fashion, 

 instead of forming a seemingly continuous excitable field — as obtains, 

 for instance, with the points yielding eye-closure in precentralis. The 

 movement is practically always bilateral, often without obvious trace of 

 preponderance of vigour for the contralateral eye. With it is associated 

 turning of the eyeballs ; almost always conjugately away from the side 

 stimulated, occasionally however convergently, and then sometimes toward 

 a plane continuous with sagittal plane of head. Sometimes the eye-opening 

 precedes the turning of the eyes, sometimes it follows it. In our experience 

 the former is more frequently the case with the lower part, e.g. 3rd frontal 

 gyrus, of the frontal region, the latter with the upper part of the region. 

 The opening of eyes tends to be followed, especially after reiterated stimula- 

 tion, not only by eyeball-turning, but by turning of the neck and head in 

 addition. This secondary and tertiary movement is always directed so as 

 to turn the face away from the side stimulated. 



In some experiments, e.g. young gorilla (fig. 12), the frontal area yield- 

 ing eye-opening seemed to be subdivided into two by an inexcitable strip 

 running horizontally across it. But considering the scattered distribution 

 of the points in this field, this subdivision may be one that more extensive 

 experimentation would break down, and certainly in some specimens it did 

 not seem confirmed. Where it occurred the lower of the two sub-fields 

 usually yielded eye-opening precedent to eye-turning, and the upper sub- 

 field eye-turning precedent to eye-opening, and not rarely altogether 

 without the latter. 



It was said above that the movement of eye-openmg seems absent from 



